Toner for developing electrostatic images

Abstract

The toner for developing electrostatic images is less likely to cause toner ejection and is excellent in printing durability. The toner includes colored resin particles and external additives. The external additives includes an external additive A and an external additive B; wherein the external additive A is silica particles being surface-hydrophobized with a specific hydrophobizing agent and having a specific number average particle diameter; and wherein the external additive B is silicone resin particles having a ratio (BS/TS) of a BET specific surface area (BS) to a theoretical specific surface area (TS) in a range of from 3.0 to 30.0, and having a specific number average particle diameter.

The invention claimed is: 
     
       1. A toner for developing electrostatic images, comprising colored resin particles that comprises a binder resin, a colorant and a charge control agent, and external additives,
 wherein the external additives contain at least an external additive A and an external additive B; 
 wherein the external additive A is silica particles being surface-hydrophobized with at least one hydrophobizing agent selected from the group consisting of a hydrophobizing agent containing an amino group, a silane coupling agent and silicone oil, and having a number average particle diameter of from 5 nm to 20 nm; 
 wherein the external additive B is silicone resin particles having a BS/TS, as an indicator of a porosity of the silicone resin particles, in a range of from 3.0 to 30.0, and having a number average particle diameter of from 0.05 μm to 1.00 μm, and wherein the BS/TS is a ratio (BS/TS) of a BET specific surface area (BS), which is measured by a gas adsorption method, to a theoretical specific surface area (TS), which is obtained by calculating from a number average particle diameter measured by scanning electron microscope (SEM) observation on a theoretical calculation formula; and 
 wherein, with respect to 100 parts by mass of the colored resin particles, a content of the external additive A is from 0.1 part by mass to 2.0 parts by mass, and a content of the external additive B is from 0.1 part by mass to 1.0 part by mass. 
 
     
     
       2. The toner for developing electrostatic images according to  claim 1 ,
 wherein the external additives further contain an external additive C; 
 wherein the external additive C is silica particles being surface-hydrophobized with at least one hydrophobizing agent selected from the group consisting of a hydrophobizing agent containing an amino group, a silane coupling agent and silicone oil, and having a number average particle diameter of from 31 nm to 200 nm; and 
 wherein a content of the external additive C is from 0.1 part by mass to 3.0 parts by mass, with respect to 100 parts by mass of the colored resin particles. 
 
     
     
       3. The toner for developing electrostatic images according to  claim 1 , wherein a water adsorption amount of the external additive B is 1.0% by mass or less. 
     
     
       4. The toner for developing electrostatic images according to  claim 1 , wherein a form of the external additive B is a spherical form. 
     
     
       5. The toner for developing electrostatic images according to  claim 2 , wherein the colored resin particles, the external additive A and the external additive C are positively chargeable, and particles of the toner are positively chargeable.